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Adult Weight Management

AWM: Portion Control (2006)


Levitsky DA, Youn T.  The more food young adults are served, the more they overeat.  J Nutr 2004; 134: 2546-2549.

PubMed ID: 15465745
Study Design:
Non-Randomized Controlled Trial
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To examine the effect of the amount of food served on the amount of food consumed by young adults, and to provide experimental evidence to support the concept that the increase in portion size may be responsible for the epidemic of overweight and obesity.
Inclusion Criteria:

Not mentioned.

Exclusion Criteria:
Those allergic to any of the foods in the study or those exhibiting a restraint score of <30 on the Stunkard restraint scale.
Description of Study Protocol:


Subjects selected from a larger pool of undergraduate students and staff who were recruited by flyers and class announcements.  Incentives for participation included free meals and extra credit for class.


Randomized Clinical Trial.

Blinding used (if applicable)

Not used.

Intervention (if applicable)

Subjects deceived into thinking that the study was about taste enhancers during week 1 and then during week 2, assigned to groups providing 100%, 125% or 150% of original amount consumed during week 1.

Statistical Analysis

ANOVA with repeated measures was used.

Data Collection Summary:

Timing of Measurements

Screened for food allergies and Stunkard restraint scale upon study entry.  Week 1 had 3 days of buffet eating to determine baseline consumption.  Week 2 had 3 days of eating at 100%, 125% or 150% of baseline consumption.

Dependent Variables

  • Weight and height measured by staff using medical scales and height measures as first test session
  • Food intake:  plates were weighed when buffet eating.
  • 7-point hunger scale:  before and after eating  

Independent Variables

  • On Monday, Wednesday and Friday of week 1 subjects were asked to record activity and breakfast, snacks and beverages eaten before lunch.  Lunch was buffet style.  Mean intake of food was used as baseline to determine 100%, 125% or 150% condition administered in week 2 on Monday, Wednesday, and Friday (not buffet).

Control Variables


Description of Actual Data Sample:

Initial N: 13 subjects, 9 male, 4 female

Attrition (final N):  See above

Age:  23 +/- 8.6 years   

Ethnicity:  Not mentioned 

Other relevant demographics:  Weight:  71.4 +/- 16.4 kg, BMI:  23.2 +/- 2.9 

Anthropometrics (e.g., were groups same or different on important measures)

Location:  Cornell University, New York 


Summary of Results:

Other Findings

Although subjects received the same food (soup, pasta, breadsticks and ice cream) in 2 weeks, intake did not decline.

The greater the amount of food subjects were served, the more they consumed with each portion size significantly different from the others (P < 0.05).

The difference in energy intake between the control intake and 125% of the control portion was 0.687 +/- 0.131 MJ (165 +/- 31 kcal) and the difference between the 125% portion and 150% portion was 0.24 +/- 0.212 MJ (105 +/- 51 kcal), P < 0.05.

The effect of serving large portion sizes was evident for all 4 components of the meal - increasing portion size increased the amount of each of the 4 foods consumed (P < 0.01).

The amount of food consumed was not associated with either the absolute hunger rating or the reduction in the hunger ratings.

Author Conclusion:
The results of the present study support the hypothesis by Young and Nestle that a major reason for the increased incidence of overweight and obesity in the US is increased food consumption caused by serving larger portion sizes.  The greater the quantity of food served to our subjects, the more they ate.  It should be possible to stop and possibly reverse the trend toward increased body weight by controlling the size of portions served to the American people.
Funding Source:
University/Hospital: Cornell University
Reviewer Comments:
Small sample size of normal weight young adults.  Total daily intake not measured - observations limited to single meal, could not see effect on subsequent intake.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) ???
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? ???
  6.6. Were extra or unplanned treatments described? ???
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes